Highly ionised plasma in the Large Magellanic Cloud: Evidence for outflows and a possible galactic wind

Abstract

Based on an analysis of the interstellar highly ionised species C IV, Si IV, N V, and O VI observed in the FUSE and HST/STIS E140M spectra of four hot stars in the Large Magellanic Cloud (LMC), we find evidence for a hot LMC halo fed by energetic outflows from the LMC disk and even possibly an LMC galactic wind. Signatures for such outflows are the intermediate and high-velocity components (v_LSR>100 km/s) relative to the LMC disk observed in the high- and low-ion absorption profiles. The stellar environments produce strong, narrow (T<20,000 K) components of C IV and Si IV associated with the LMC disk; in particular they are likely signatures of H II regions and expanding shells. Broad components are observed in the profiles of C IV, Si IV, and O VI with their widths implying hot, collisionally ionised gas at temperatures of a few times 100,000 K. There is a striking similarity in the O VI/C IV ratios for the broad LMC and high-velocity components, suggesting much of the material at v_LSR>100 km/s is associated with the LMC. The velocity of the high-velocity component is large enough to escape altogether the LMC, polluting the intergalactic space between the LMC and the Milky Way. The observed high-ion ratios of the broad LMC and high-velocity components are consistent with those produced in conductive interfaces; such models are also favored by the apparent kinematically coupling between the high and the weakly ionised species.